And now those of us who go to movies hoping to get scared out of our seats are offered Insidious: Chapter 3, which opens Friday.

Insidious refers to something that is "slowly and secretly causing harm," and certainly Insidious: Chapter 3's story of a girl who manages to summon an evil spirit when she reaches out to what she thinks is the ghost of her recently deceased mother will cement the meaning of this word in our brains forever.

But just in case you want to brush up on the word's nuances before heading to the film, check out the blurb from the insidious page in our Dictionary.

And remember not to confuse insidious with the similar-sounding invidious. As we explain here:

Insidious describes something that lies in wait to get you...invidious doesn't hide; it's hateful right away.

Though come to think of it, either one might have made a fitting way to title the over-the-top spiritual evil portrayed by this film.